Computational Analysis of Tetragonal ThH2 Hydride: Structural, Electronic, Mechanical, Thermodynamic, and Hydrogen Storage Capabilities for Future Energy Applications

In this study, a comprehensive first-principles investigation has been carried out on ThH2 to evaluate its structural, electronic, elastic, phonon, thermodynamic, and hydrogen storage properties. The calculations were performed using DFT within the framework of the GGA-PBE approximation, employing the CASTEP module. Structural optimization confirmed that ThH2 crystallizes in a bct phase with space group I4/mmm, and the lattice parameters show good agreement with available experimental and computational data. Electronic band structure and DOS analyses reveal metallic behavior, with significant hybridization between Th-6d and H-1s orbitals. The elastic constants satisfy the mechanical stability criteria and indicate that ThH2 is ductile and elastically anisotropic. Phonon dispersion confirms the dynamical stability of the compound, with no imaginary frequencies across the Brillouin zone. Temperature-dependent thermodynamic properties such as Debye temperature, Helmholtz free energy, entropy, enthalpy, and heat capacity were also evaluated using the quasi-harmonic approximation. The volumetric hydrogen storage capacity of ThH2 (82.57 kg/m3) significantly exceeds the U.S. DOE’s 2025 target of 40 kg H2/m3, demonstrating its strong potential to meet and surpass future storage requirements. The findings establish ThH2 as a thermodynamically stable and mechanically robust material, making it a promising candidate for applications in advanced nuclear fuel systems and storage technologies.